An apparatus and application for simulating and evaluating the electrical characteristics of the interface of a cable accessory

Abstract

The present invention discloses a device and application for simulating and evaluating the electrical characteristics of the interface of cable accessories, belonging to the technical field of cable detection. Through the design of the upper and lower electrode structures and coaxially stacking them at the interface of the double-layer dielectric, an orthogonal electric field is constructed, simulating the experimental conditions of the orthogonal electric field borne by the interface of the insulating material used for cable accessories. Further, by selecting the electrode size, the ratio of the axial electric field component and the tangential electric field component of the orthogonal electric field can also be adjusted, thereby simulating the electric field borne by the interface between the enhanced insulation and the cable body insulation in different specifications of cable accessories. Compared with the existing traditional test methods that can only provide a single electric field component, it has the advantage of being closer to the electric field distribution conditions of the cable accessory working conditions, so that the electrical characteristics of the interface of the insulating material used for cable accessories under the combined action of the axial electric field component and the radial electric field component can be tested and analyzed more accurately.

Description

Technical Field

[0001] The invention relates to a simulation and evaluation device for electrical characteristics of a cable accessory interface and an application thereof, belonging to the technical field of cable detection. Background Art

[0002] In high-voltage power equipment, partial discharge, as a typical form of electrical aging, often occurs in insulation defects or places with dense electric fields. Since it does not penetrate the insulation and the discharge energy is small, the impact in a short period of time is not obvious. However, the long-term accumulation of partial discharge will cause the degradation of the insulation material, resulting in a decrease in insulation strength and eventually breakdown.

[0003] High-voltage cables are widely used power equipment, and people have extremely strict requirements on their working reliability. High-voltage cable accessories are an important part of high-voltage cable lines, and are also the weakest link. Most of the faults in high-voltage cable lines come from cable accessories such as cable accessories and cable terminals. In the insulation structure of high-voltage cables, the electric field distribution is mainly radial, and there are almost no electric field components in other directions. However, at the installation site of cable accessories, the outer semi-conductive layer of the cable is cut off, which distorts the electric field distribution, and inevitably generates an axial electric field at the interface between the enhanced insulation and the cable body insulation. The insulation interface has a seriously low breakdown strength relative to the two material bodies that constitute the interface, so it is more likely to discharge or surface breakdown. In the failure of cable accessories, the insulation interface discharge problem between the enhanced insulation and the cable body insulation is a technical problem that needs to be solved urgently. It not only increases the design difficulty of cable accessories, but also has a serious impact on the long-term working reliability of cable accessories.

[0004] The insulation structure of cable accessories is complex, and there are interfaces of multiple materials. The insulation interface formed by the enhanced insulation and the cable body insulation is the part with the most concentrated electrical stress distribution. Through long-term research and practice, it is found that the discharge phenomenon of the insulation interface is jointly determined by the axial electric field component (parallel to the interface) and the radial electric field component (perpendicular to the interface). Due to the different dielectric parameters (conductivity and relative dielectric constant, etc.) of the enhanced insulation and the cable body insulation materials, in this composite insulation structure composed of multiple layers of dielectrics, under the action of the radial electric field, trapped space charges or interface polarization charges will accumulate at the insulation interface, resulting in local distortion of the electric field at the insulation interface; and under the action of the axial electric field, the charge can be quickly transmitted along the interface direction. When the electric field component is large enough, the charge transmission process along the interface is intensified, which will cause local discharge along the interface direction or even surface breakdown. Therefore, it can be seen that the discharge problem of the insulation interface of cable accessories is a very complex physical process under the action of orthogonal electric fields.

[0005] In addition, during the installation or manufacturing of cable accessories, defects such as air gaps, scratches, impurities, and microcracks may also exist at the insulation interface. These factors lead to a further reduction in the electrical withstand strength at the insulation interface, making it more likely to occur partial discharge, and also making the interface discharge process more complex.

[0006] The electrical characteristics of the insulation interface of cable accessories are important factors determining the long-term working reliability of cable systems. Understanding the electrical characteristics of the insulation material interface for cable accessories has important reference value for material research and development and accessory design. However, there is a lack of feasible methods for evaluating the electrical characteristics of the insulation material interface for cable accessories in the existing technology.

[0007] Theoretically analyzed, if the "cylindrical" enhanced insulation and "flare-shaped" stress cone structures similar to the actual cable insulation and cable accessory insulation structures are adopted, an orthogonal electric field similar to the working conditions of cable accessories can also be created. However, the manufacturing of enhanced insulation and stress cones requires a lot of time and funds to customize molds, and the process cycle of manufacturing specimens is too long. This method is not only inefficient and uneconomical, but also difficult to conduct targeted test analysis on its interface electrical characteristics. It is not applicable to the early-stage research and development in the laboratory, but only applicable to actual production.

[0008] Under laboratory conditions, researchers often use "sheet-shaped" specimens to study the electrical characteristics of the insulation interface. However, the existing technology often simply uses the body electric field perpendicular to the specimen (which can be equivalent to the radial electric field) or the surface electric field parallel to the specimen surface (which can be equivalent to the axial electric field), but fails to uniformly and controllably create an orthogonal electric field. Since the electric field distribution of cable accessories under normal working conditions cannot be simulated, and the mutual influence between the axial electric field and the radial electric field is ignored, only one-sided information of the insulation interface can be obtained by using the existing test devices or methods, and the true electrical characteristics of the insulation interface under the orthogonal electric field cannot be known. This will lead to a lack of sufficient and reliable scientific basis in the process of research and development of insulation materials for cable accessories and the design of the geometric structure of cable accessories.

[0009] Therefore, it is very necessary to provide an accurate, efficient, and economical device and application for simulating and evaluating the electrical characteristics of the cable accessory interface for the research and development of cable accessories with higher voltage levels and better working reliability in the future. Summary of the Invention

[0010] The present invention provides an evaluation device and method for the electrical characteristics of the insulation material interface for cable accessories under an orthogonal electric field, aiming to simulate the key working conditions of the cable accessory insulation interface in the simplest, efficient, and economical way, construct an orthogonal electric field, and conduct test analysis and evaluation on the interface formed by the insulation material for cable accessories under the orthogonal electric field, so as to provide a more scientific research method and reference basis for the research and development of insulation materials for cable accessories and the geometric structure design of cable accessories.

[0011] The technical method of the present invention:

[0012] One of the purposes of the present invention is to provide a device for simulating the electrical characteristics of the interface of cable accessories, the device comprising an upper block and a lower block coaxially stacked up and down, the upper block and the lower block being epoxy resin blocks of the same size and respectively having an upper electrode and a lower electrode built therein, the upper electrode being a cover structure, the lower electrode being a cylindrical structure with an arc surface at one end, the upper electrode and the lower electrode being connected to an external spherical cap via wiring posts, respectively.

[0013] It is further defined that the upper electrode is an integrated cover structure formed by a circular ring and a circular plate coaxially, the circular plate cover is mounted on the circular ring, and the diameter of the circular plate is slightly smaller than the outer diameter of the circular ring.

[0014] It is further defined that the upper electrode and the lower electrode are both parallel to and in contact with the contact surfaces of the upper block and the lower block.

[0015] It is further defined that sample one and sample two are arranged in sequence between the upper block and the lower block, and the contact surfaces between sample one and the upper block, and between sample two and the lower block are evenly coated with a silicone oil layer.

[0016] It is further defined that the sample 1 and the sample 2 are discs of the same size, coaxially stacked and in close contact.

[0017] It is further defined that sample 1 and sample 2 are two types of insulating materials, simulating cable accessory reinforced insulation and cable accessory reinforced insulation respectively.

[0018] It is further defined that the sample 1 is the vulcanized silicone rubber or EPDM rubber.

[0019] It is further defined that sample 2 is cross-linked polyethylene or polypropylene.

[0020] It is further defined that the upper block and the lower block are both cylinders and are coaxially arranged with the upper electrode and the lower electrode respectively.

[0021] The second object of the present invention is to provide an evaluation device for the electrical characteristics of the cable accessory interface, the device comprising the above-mentioned simulation device for the electrical characteristics of the cable accessory interface, HFCT (high frequency current sensor), oscilloscope, picoammeter, toggle switch, power supply and host computer;

[0022] The lower electrode of the simulation device is connected to the output end of the power supply through an external ball cap, and the upper electrode is grounded through the external ball cap via a ground wire and a button switch. The ground wire passes through the measuring coil of the HFCT, and the signal output end of the HFCT is connected to the oscilloscope. After the oscilloscope is connected to the host computer, it forms a loop with the power supply.

[0023] It is further defined that one pin of the button switch is a ground electrode, the common pin is connected to the ground wire, the other pin is connected to the picoammeter, and the picoammeter is connected to the host computer to form a loop with the power supply.

[0024] A third object of the present invention is to provide a method for using an evaluation device for the electrical characteristics of the interface of the above cable accessory, and the method includes the following steps:

[0025] (1) Stack the upper block, specimen 1, specimen 2, and lower block coaxially from top to bottom in sequence, and evenly apply a silicone oil layer on the contact surfaces between specimen 1 and the upper block, and between specimen 2 and the lower block, and connect the circuit;

[0026] (2) Toggle the toggle switch to form a circuit, start the test, control the power supply, increase the voltage at a rate of 0.1 kV / s. When the oscilloscope detects partial discharge, the upper computer records the output voltage of the power supply at this time as the partial discharge inception voltage PDIV. Continue to increase the voltage. When the output voltage of the power supply reaches 1.1 times PDIV, decrease the voltage at a rate of 0.1 kV / s. When the oscilloscope detects the end of partial discharge, the upper computer records the output voltage of the power supply at this time as the partial discharge extinction voltage PDEV.

[0027] Further defined, during the entire test process, the upper computer records in real time the partial discharge signal waveforms and leakage currents measured by the HFCT and picoammeter, and further obtains the electrical characteristic information of the electrical phase distribution map and discharge frequency through the analysis of the partial discharge signal waveforms.

[0028] Further defined, the interface between specimen 1 and specimen 2 can be subjected to various forms of surface treatment such as grinding or pressure can be provided by an external pressure device to simulate different forms of cable accessories.

[0029] Beneficial effects:

[0030] (1) Through the design of the upper electrode and lower electrode structures, the present invention constructs an orthogonal electric field at the interface of the double-layer dielectric by coaxially stacking, simulates the experimental conditions of the orthogonal electric field borne by the interface of the insulating material for cable accessories. Further, by selecting the electrode size, the ratio of the axial electric field component (perpendicular to the interface) and the tangential electric field component (parallel to the interface) of the orthogonal electric field can also be adjusted, so as to simulate the electric field borne by the interface between the enhanced insulation and the cable body insulation in different specifications of cable accessories. Compared with the existing traditional test methods that can only provide a single electric field component, it has the advantage of being closer to the electric field distribution condition of the cable accessory working condition, and thus can more accurately test and analyze the electrical characteristics of the interface of the insulating material for cable accessories under the combined action of the axial electric field component (parallel to the interface) and the radial electric field component (perpendicular to the interface).

[0031] (2) The present invention uses epoxy resin to encapsulate the electrodes, and the edges of the electrodes are rounded. The wiring ends of the electrodes all adopt a spherical structure, which effectively equalizes the electric field distribution at the edges of the electrodes, avoids the interference of stray discharge signals at the edges of the electrodes on the test results, makes the anti-interference ability of the test process stronger, and makes the test results more reliable.

[0032] (3) Compared with the embedded metal foil electrodes, the present invention uses non-embedded electrodes, which not only has various advantages such as convenient, fast, and reusable use, but also avoids the specimen deformation caused by electrode embedding and the discharge that occurs at the irregular interface between the embedded electrode and the material.

[0033] (4) The electrode design of the present invention ensures the flatness of the insulation interface. And compared with the extremely uneven field shaped by the metal foil electrodes, the field shaped by the present invention is relatively more uniform and stable, which is more in line with the working conditions of actual cable accessories.

[0034] (5) The present invention constructs an orthogonal electric field at the double-layer dielectric interface by stacking the cover structure electrode and the cylindrical structure electrode with one end face being an arc surface, so that on the insulation interface, the axial electric field and the tangential electric field on each concentric circle circumference with the interface center as the center point are equal in magnitude, which is equivalent to increasing the tested area of the material interface under the same electric field, and is more conducive to expressing the overall characteristics of the material interface, making the test results more representative and statistically valuable.

[0035] (6) The present invention simultaneously uses a picoammeter to measure the leakage current under the orthogonal electric field and a high-frequency current sensor HFCT to measure the partial discharge signals in the specimen under the orthogonal electric field. These two test methods are controlled by a switch and can be carried out simultaneously, so that the two test signals support and verify each other, or can be carried out separately, with convenient operation and high flexibility. And it is possible to simultaneously obtain various electrical characteristic information such as the leakage current, partial discharge inception voltage, partial discharge extinction voltage, discharge phase distribution diagram, discharge frequency, etc. under the orthogonal electric field of the insulation material interface for cable accessories. Further, the advantages and disadvantages of the interface are quantitatively evaluated in two forms of partial discharge and leakage current, providing a variety of scientific reference data for the research and development of cable accessory materials and the geometric structure design.

[0036] (7) The evaluation method under the orthogonal electric field of the insulation interface provided by the present invention is applicable to the research and development of cable accessories. It can realize the electrical characteristic analysis of the insulation material interface for cable accessories under the working condition electric field in an economical and efficient manner under laboratory conditions, and can also quantitatively obtain the key electrical performance parameters of the material interface. Based on the data obtained by the present invention, not only can the modification effect of a certain material be evaluated, but also for a determined insulation material, its discharge inception voltage, extinction voltage and other parameters can be determined, providing parameters for the geometric structure design of cable accessories. Description of the Drawings

[0037] Figure 1 Schematic diagram of the three-dimensional structure of the simulation device for the electrical characteristics of the cable accessory interface provided by the present invention;

[0038] Figure 2 Cross-sectional view of the simulation device for the electrical characteristics of the cable accessory interface provided by the present invention;

[0039] Figure 3 Schematic diagram of the evaluation device for the electrical characteristics of the cable accessory interface provided by the present invention;

[0040] Figure 4 Schematic diagram of the simulation model of the simulation device in the embodiment;

[0041] Figure 5 Electric field simulation result of the simulation device in Embodiment 1;

[0042] Figure 6 Electric field simulation result of the cable accessory interface in Embodiment 1;

[0043] Figure 7 Electric field nephogram of the simulation device in Embodiment 1;

[0044] Figure 8 Electric field nephogram of the cable accessory interface in Embodiment 1;

[0045] Figure 9 Relationship between the arc surface radius of the lower electrode and the tangential component of the electric field at the cable accessory interface;

[0046] Figure 10 Relationship between the arc surface radius of the lower electrode and the axial component of the electric field at the cable accessory interface;

[0047] Figure 11 Relationship between the ring radius of the upper electrode and the tangential component of the electric field at the cable accessory interface;

[0048] Figure 12 Relationship between the ring radius of the upper electrode and the axial component of the electric field at the cable accessory interface;

[0049] Figure 13 Electric field intensity nephogram and electric field equipotential lines at the interface;

[0050] In the figure, 1 - upper layer block, 1-1 - upper electrode, 2 - lower layer block, 2-1 - lower electrode, 3 - specimen 1, 4 - specimen 2, 5 - external spherical cap, 6 - HFCT, 7 - oscilloscope, 8 - picoammeter, 9 - toggle switch, 10 - power supply, 11 - host computer. Specific implementation manners

[0051] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and should not be construed as indicating or implying relative importance.

[0053] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0054] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0055] Specific Embodiment 1

[0056] As Figures 1 - 2As shown, the simulation device of the electrical characteristics of the cable accessory interface includes an upper block 1 and a lower block 2 coaxially stacked up and down, the upper block 1 and the lower block 2 are epoxy resin blocks of the same size and respectively built with an upper electrode 1-1 and a lower electrode 2-1, the upper electrode 1-1 is an integrated cover structure composed of a circular ring and a circular plate coaxially, the circular plate cover is installed on the circular ring, and the diameter of the circular plate is slightly smaller than the outer diameter of the circular ring; the lower electrode 2-1 is a cylindrical structure with an arc surface at one end, the upper electrode 1-1 and the lower electrode 2-1 are respectively connected to the external ball cap 5 through a terminal, and the upper electrode 1-1 and the lower electrode 2-1 are parallel to and in contact with the contact surface of the upper block 1 and the lower block 2. The upper block 1 and the lower block 2 are both cylindrical, and are respectively coaxially arranged with the upper electrode 1-1 and the lower electrode 2-1. In this way, the upper electrode 1-1 and the lower electrode 2-1 are encapsulated in epoxy resin to avoid discharge caused by the electrode shape and surface burrs, and the upper electrode 1-1 and the lower electrode 2-1 are provided with terminals on their sides, which penetrate the encapsulated epoxy resin and are provided with external ball caps 5 at the ends to avoid discharge. The upper block 1 and the lower block 2 are both cylinders, and the two have the same size to ensure that the upper electrode 1-1 and the lower electrode 2-1 are coaxially arranged. Further, the cover structure electrode and the cylindrical structure electrode with an arc surface at one end face are stacked on the double-layer dielectric interface to construct an orthogonal electric field, and the combined effect of the radial electric field and the axial electric field is comprehensively considered, which is more in line with the working conditions of the insulation interface under normal conditions, and an electric field distribution similar to the insulation interface of the real cable accessories is shaped on the insulation interface, and the axial electric field (perpendicular to the interface) and the tangential electric field (parallel to the interface) on the circumference of each concentric circle with the center of the interface as the center are equal in size, which increases the measured area of ​​the sample.

[0057] Sample 1 3 and sample 2 4 are arranged in sequence between the upper block 1 and the lower block 2, and the contact surface between sample 1 3 and the upper block 1, sample 2 4 and the lower block 2 is evenly coated with a silicone oil layer. Sample 1 3 and sample 2 4 are discs of the same size, coaxially stacked and in close contact. In this way, sample 1 3 and sample 2 4 are two insulating materials, respectively, simulating cable accessory enhanced insulation and cable accessory enhanced insulation. Sample 1 3 and sample 2 4 are the same size, coaxially stacked, and in close contact, and the insulating interface formed is the cable accessory interface. Further, the interface between sample 1 3 and sample 2 4 can be subjected to various forms of surface treatment such as grinding or pressure (0.1-0.4MPa) provided by an external pressure device to simulate different forms of cable accessories, and a silicone oil layer is evenly coated on the contact surface between sample 1 3 and the upper block 1, sample 2 4 and the lower block 2 to expel air and avoid discharge at the interface.

[0058] like Figure 3As shown in the figure, the evaluation device for the electrical characteristics of the cable accessory interface includes the simulation device for the electrical characteristics of the cable accessory interface, HFCT, oscilloscope 7, picoammeter 8, toggle switch 9, power supply 10, and host computer 11. Among them, the lower electrode 2-1 of the simulation device is connected to the output terminal of the power supply 10 through an external spherical cap 5, and the upper electrode 1-1 is grounded through the external spherical cap 5, the ground wire, and the toggle switch 9. The ground wire passes through the measuring coil of the HFCT 6, and the signal output terminal of the HFCT 6 is connected to the oscilloscope 7. After the oscilloscope 7 is connected to the host computer 11, a loop is formed with the power supply 10. One pin of the toggle switch 9 is connected to the ground electrode, the common pin is connected to the ground wire, and the other pin is connected to the picoammeter 8. After the picoammeter 8 is connected to the host computer 11, a loop is formed with the power supply 10. With such a setting, the power supply 10 is a high-voltage adjustable power supply, which is connected to the lower electrode 2-1 to achieve adjustable voltage. By toggling the toggle switch 9, the picoammeter 8 can be connected in series with the upper electrode 2-1 to measure the leakage current between the upper electrode 1-1 and the lower electrode 2-1. The power supply 10, oscilloscope 7, and picoammeter 8 are all connected to the host computer 11. The host computer 11 controls the power supply 10 to adjust the voltage through a program, and at the same time collects and records the electrical signals collected by the oscilloscope 7 and the picoammeter 8, and electrical characteristic information such as the partial discharge inception voltage, partial discharge extinction voltage, discharge phase diagram, discharge frequency, and leakage current can be obtained.

[0059] The usage method of the above evaluation device for the electrical characteristics of the cable accessory interface includes the following steps:

[0060] (1) Stack the upper block 1, sample 1 3, sample 2 4, and lower block 2 coaxially from top to bottom in sequence, and evenly apply a silicone oil layer on the contact surfaces between sample 1 3 and the upper block 1, and between sample 2 4 and the lower block 4. Connect the circuit according to Figure 3 Connect the circuit;

[0061] (2) Toggle the toggle switch 9 to form a circuit, start the test, control the power supply 10, and increase the voltage at a rate of 0.1 kV / s. When the oscilloscope 7 detects partial discharge, the host computer 11 records the output voltage of the power supply 10 at this time as the partial discharge inception voltage PDIV. Continue to increase the voltage. When the output voltage of the power supply 10 reaches 1.1 times PDIV, reduce the voltage at a rate of 0.1 kV / s. When the oscilloscope 7 detects the end of partial discharge, the host computer 11 records the output voltage of the power supply 10 at this time as the partial discharge extinction voltage PDEV. And during the whole test process, the host computer 11 records the partial discharge signal waveforms and leakage current measured by the HFCT 6 and the picoammeter 8 in real time, and further obtains electrical characteristic information such as the electrical phase distribution diagram and discharge frequency through the analysis of the partial discharge signal waveforms.

[0062] Example 1

[0063] (1) Prepare one sample of sample 1 (vulcanized ethylene propylene rubber) and one sample of sample 2 (crosslinked polyethylene) flat insulation samples, both with the same size (a circular sample with a radius of 50 mm and a thickness of 200 μm). Grind the contact surfaces of the two samples, and then clean the electrode surfaces of sample 1, sample 2, upper block 1, and lower block 2 using ethanol.

[0064] (2) Stack the upper block 1, sample 1, sample 2, and lower block 2 coaxially from top to bottom in sequence, and evenly apply a silicone oil layer on the contact surfaces between sample 1 and upper block 1, and between sample 2 and lower block 4, while ensuring that the upper electrode 1-1 built into the upper block 1 and the lower electrode 2-1 built into the lower block 2 are coaxial.

[0065] (3) Connect the lower electrode 2-1 to the output terminal of the power supply 10 through an external spherical cap 5, connect the upper electrode 1-1 to the ground through an external spherical cap 5 via a ground wire and a toggle switch 9. The ground wire passes through the measurement coil of the HFCT 6, and the signal output terminal of the HFCT 6 is connected to the oscilloscope 7. After the oscilloscope 7 is connected to the upper computer 11, it forms a loop with the power supply 10. One pin of the toggle switch 9 is connected to the ground electrode, the common pin is connected to the ground wire, and the other pin is connected to the picoammeter 8. After the picoammeter 8 is connected to the upper computer 11, it forms a loop with the power supply 10.

[0066] To further verify the accuracy of the evaluation device provided in this embodiment, a finite element simulation software is used to perform modeling and simulation on the electrode and cable accessories, and the simulation results are compared.

[0067] First, a two-dimensional axisymmetric model is used to simulate the simulation device. The simulation model is as Figure 4 shown. In the model, the voltages applied to the upper electrode 1-1 and the lower electrode 2-1 are 30 kV, and the material parameters of the model are shown in Table 1 below:

[0068] Table 1

[0069] Structure Relative permittivity Upper electrode, lower electrode 1000 Epoxy resin 4.95 Vulcanized ethylene propylene rubber 2.7 Crosslinked polyethylene 2.3

[0070] The simulation results are as Figures 5 - 8 shown. As can be seen from the figure, the above evaluation device can construct an orthogonal electric field at the interface of the double-layer insulating medium (composed of vulcanized ethylene propylene rubber and crosslinked polyethylene), and this orthogonal electric field can better simulate the electric field at the insulation interface of the cable accessory (composed of the enhanced insulation of the cable accessory and the insulation of the cable body).

[0071] Simulate the interface electric field intensity cloud map and electric field equipotential lines of the simulation device. The results are as Figure 13 shown. As can be seen from Figure 13 it, when the upper electrode and the lower electrode remain coaxial, it can ensure that on all concentric circles centered on the interface center, the axial electric field and the tangential electric field are equal in magnitude.

[0072] Since cable accessories come in a variety of sizes, their geometric parameters have a significant impact on the orthogonal electric field at the insulation interface between the reinforced insulation and the cable body insulation. Therefore, based on the above, this embodiment further changes the radius of the upper electrode ring and the radius of the lower electrode arc surface to change the ratio of the axial electric field to the tangential electric field at the insulation interface. This embodiment simulates cable accessories of different sizes by changing the radius of the upper electrode ring and the radius of the lower electrode arc surface. The simulation results are shown in Figure 2. Figures 9 - 12 As shown in the figure, it can be seen that increasing the radius of the upper electrode ring and the radius of the lower electrode arc surface can reduce the peak values ​​of the axial component and tangential component of the electric field on the interface, and increasing the radius of the lower electrode arc surface can make the peak positions of the axial component and tangential component of the electric field on the interface move away from the lower electrode. By changing the radius of the upper electrode ring and the radius of the lower electrode arc surface, the size and distribution of the orthogonal electric field on the interface can be changed to simulate cable accessories of different sizes.

[0073] Finally, it should be noted that the embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An analog device for the electrical characteristics of the interface of a cable accessory, characterized in that It includes an upper block and a lower block stacked coaxially up and down. The upper block and the lower block are epoxy resin blocks with the same size and internally provided with an upper electrode and a lower electrode respectively. The upper electrode is a cover body structure, and the lower electrode is a cylindrical structure with an arc-shaped end face. The upper electrode and the lower electrode are respectively connected to an external ball cap through a terminal; The upper electrode is an integrated cover body structure composed of a coaxial ring and a circular plate. The circular plate is mounted on the ring, and the diameter of the circular plate is smaller than the outer diameter of the ring; Both the upper electrode and the lower electrode are parallel to and in contact with the contact surfaces of the upper block and the lower block; A sample one and a sample two are sequentially arranged between the upper block and the lower block, and silicone oil layers are evenly applied to the contact surfaces of the sample one and the upper block, and the sample two and the lower block; The sample one and the sample two are circular wafers with the same size, stacked coaxially and in close contact.

2. The simulation device according to claim 1, wherein Both the upper block and the lower block are cylinders, and are coaxially arranged with the upper electrode and the lower electrode respectively.

3. An evaluation device for the electrical characteristics of the interface of a cable accessory, characterized in that It includes the simulation device according to any one of claims 1 to 2, an HFCT, an oscilloscope, a picoammeter, a toggle switch, a power supply and a host computer; The lower electrode of the simulation device is connected to the output end of the power supply through an external ball cap, the upper electrode is grounded through an external ball cap via a ground wire and a toggle switch, the ground wire passes through the measurement coil of the HFCT, and the signal output end of the HFCT is connected to the oscilloscope. After the oscilloscope is connected to the host computer, a loop is formed with the power supply.

4. The evaluation device according to claim 3, wherein One pin of the toggle switch is connected to the ground electrode, the common pin is connected to the ground wire, and the other pin is connected to the picoammeter. After the picoammeter is connected to the host computer, a loop is formed with the power supply.

5. A method for using the evaluation device according to any one of claims 3 to 4, characterized in that It includes: (1) Stack the upper block, the sample one, the sample two and the lower block coaxially from top to bottom in sequence, evenly apply silicone oil layers to the contact surfaces of the sample one and the upper block, and the sample two and the lower block, and connect the circuit; (2) Toggle the toggle switch to form a path, start the test, control the power supply, boost the voltage at a boosting rate of 0.1 kV / s. When the oscilloscope detects partial discharge, the host computer records the output voltage of the power supply at this time as the partial discharge inception voltage PDIV. Continue to boost the voltage. When the output voltage of the power supply reaches 1.1 times PDIV, reduce the voltage at a voltage reduction rate of 0.1 kV / s. When the oscilloscope detects the end of partial discharge, the host computer records the output voltage of the power supply at this time as the partial discharge extinction voltage PDEV.

6. The method of use according to claim 5, wherein During the whole test process, the host computer records the partial discharge signal waveforms and leakage currents measured by the HFCT and the picoammeter in real time, and further obtains the electrical characteristic information such as the electrical phase distribution map and the discharge frequency through the analysis of the partial discharge signal waveforms.

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